Antimicrobial drugs, and especially antibiotics, have developed remarkably. In contrast, antifungal drugs are lacking in variety and effectiveness. In particular, the opportunistic mycoses of internal organs caused by infections with Candida, Aspergillus, and Cryptococcus due to a decreased bodily defense capability resulting from extensive administration of carcinostatic agents, immunosuppressants, steroid hormones, and acquired immunodeficiency syndrome (AIDS) in recent years are posing significant medical problems. Therefore, there is a strong demand for developing drugs for mycoses.
Biologically active agents contained in mushrooms have been examined in various ways since early times. Ganoderma applanatum, and Coriolus versicolor have been conventionally used as oriental drugs and folk remedies effective for stomach, esophageal, mammary, and prostate cancers. In particular, .beta.-D-glucan-protein complex (PS-K) extracted from cultured mycelium from Corliolus versicolor has been used widely as an anticancer medicament. It was reported in Korea that Lee et al. (1981) and Kim et al. (1982) obtained from Cryptoporus volvatus a protein-polysaccharide with anticancer activity from water extract and ergosterol from chloroform-methanol extract (Asakawa et al., Trans. Mycol. Soc. Japan 29: 281-296, 1998). Asakawa et al. reported obtaining various derivatives of cryptoporic acid as bitter elements from the Cryptoporus volvatus and that Cryptoporic acid different from those mentioned above has been obtained from culture extracts (M. Hirotani et al., Phytochemistry 30(5), 1555-1559 (1991)). It has also been reported that cryptoporic acid derivatives can be obtained from cultured Ganoderma neojaponicum. Furthermore, other cryptoporic acid derivatives and compounds analogous to cryptoporic acid derivatives are reported to have been obtained from Haploporus odorus (Y. Morita et al., Biosci. Biotech. Biochem. 59(19): 2008-2009 (1995)).
Biological activities of cryptoporic acid reportedly include active oxygen inhibitory activity (Asakawa et al., Trans. Mycol. Soc. Japan 29: 281-296, 1988), inhibition of germination of rice (T. Hashimoto et al., Tetrahydron Lett. 28(50): 6303-6304 (1987)), and an inhibitory effect on chemical carcinogenesis (T. Narisawa et al., Jpn. J. Cancer Res. 83: 830-834 (1992)).
Cryptoporic acid derivatives described above with partially known properties form a group of compounds described by formula 4. ##STR1## wherein R.sup.4 represents a hydrogen atom or a hydroxyl group, and R.sup.1, R.sup.2, and R.sup.3 may be the same or different from each other and each represents a hydrogen atom, an alkyl group (particularly a lower alkyl group, more specifically a methyl group), and an alkali metal such as sodium or potassium.